Telomerase is a ribonucleoprotein complex responsible for extending the dG-rich strand of the telomere terminal repeats. It employs a small segment of a stably associated RNA component as template, and pre-existing chromosomal ends as primers to accomplish reverse transcription. Telomerase activity isspecifically activated in cancer cells, and promotes neoplastic transformation by endowing cells with unlimited replicative potential. Selective inactivation of telomerase in tumor cells leads to telomere shortening and apoptosis, validating the potential of telomerase inhibitors in anti-cancer therapy. The goal of this research is to investigate telomerase regulation and function in Candida albicans, a relatively unexplored experimental system. In contrast to other well-studied fungi, Candida possesses longer telomere tracts, a regular extended telomere repeat, and exhibits more active recombination at telomeres. Because of these unusual features, we have been able to develop unique biochemical and molecular toolsfor addressing fundamental issues in the field. Most importantly, we have been able to demonstrate for the first time the effects of two regulatory factors on telomerase activity in vitro, and are thus in a position to approach telomerase regulation using the powerful combination of yeast genetics and biochemistry. Our preliminary studies suggest two major hypotheses: (1) the CaEstlp and CaEst3p subunit of the telomerase complex can activate telomerase function through protein-protein and/or protein-DNA interaction, and (2) some telomerase subunits can participate in the protection of telemere ends independent of their telomere extension function. To examine these hypotheses, we will utilize a series of biochemical, genetic, and cell biological assays to analyze Candida telomeres and telomerase inappropriate mutant strains. We will also develop purified in vitro systems to assess telomerase activation by regulatory factors, and to investigate relevant protein-DNA and protein-protein interactions. We anticipate that our findings will contribute to a detailed molecular understanding of telomerase function and regulation.